1. Field of the Invention
The present invention relates generally to a receiving device and method for CDMA communication systems, and in particular, to a device and method for measuring non-orthogonal noise power of a received channel signal.
2. Description of the Related Art
Code division multiple access (CDMA) communication systems use orthogonal codes for channel separation. In particular, a forward link typically employs a synchronous CDMA technique which separates users with the orthogonal codes. In a non-multi-path environment, there is no interference among the channels using different orthogonal codes. Even in the multi-path environment, an orthogonality among the respective channels is maintained with respect to the multi-path signal components. Therefore, although some of the signals input to the respective fingers act as interference, most of the signals do not act as interference.
Accordingly, to implement an effective CDMA communication system, it is necessary to accurately measure the signal components acting as interference, i.e., non-orthogonal noise power. The measured non-orthogonal noise power can be used to determine a signal-to-interference ratio (SIR) for controlling gains of the fingers in a receiving device.
A method for measuring the non-orthogonal noise power is disclosed in U.S. Pat. No. 5,559,790 (hereinafter xe2x80x9cthe ""790 patentxe2x80x9d) issued to Yano et al. In the disclosed non-orthogonal noise measuring method, a specified orthogonal code from the available orthogonal codes for the forward link is not assigned to the forward link. A base station sends information about the non-assigned orthogonal code to the mobile stations. The mobile stations then despread the received channel signal on the forward link with the assigned orthogonal codes, and calculate the energy component of the despread channel signal to detect a non-orthogonal noise component.
In the configuration described in the ""790 patent, since a specific orthogonal code is assigned to the forward link for measurement of the non-orthogonal noise power, the specific orthogonal code cannot be used for the other channels. That is, even when additional orthogonal codes may be required to increase the efficiency of the forward link, the specified orthogonal code cannot be used. Furthermore, in the IS-95 standard, it is impossible to use the specific code in measuring the non-orthogonal noise power.
In addition, U.S. Pat. No. 5,754,533 issued to Bender et al. discloses another non-orthogonal noise measuring method wherein a receiving device estimates the energy detected by despreading a received signal on a channel having a low signal power as a non-orthogonal noise component (or power). Here, the channel having the low signal power is an IS-95 sync channel. However, this non-orthogonal noise measuring method estimates a value obtained by adding a sync channel data signal component, no matter how low it is, to the non-orthogonal noise power. So, it is impossible to accurately measure the non-orthogonal noise power.
It is, therefore, an object of the present invention to provide a device and method for measuring, at a receiving device, a non-orthogonal noise component included in a signal transmitted from a transmitting device in a CDMA communication system.
It is another object of the present invention to provide a device and method for measuring a non-orthogonal noise component from a repetition pattern for a channel where the same data is repeated, in a CDMA communication system.
It is a further object of the present invention to provide a device and method for measuring a non-orthogonal noise component from a repetition pattern for a traffic channel of low rate, in a CDMA communication system.
To achieve the above objects, there is provided a non-orthogonal noise detecting device for a CDMA communication system. The device comprises a despreader for despreading multiple channel signals including a specific channel with an orthogonal code assigned to the specific channel repeating at least two same second symbols at a given first symbol duration, to generate despread repeated symbols; a difference signal generator for receiving the despread second symbols, and generating a difference signal between a presently received second symbol and a previously received signal second symbol; and a noise detector for converting the difference signal to an energy value to generate a non-orthogonal noise signal.